Fixes bug in DnsCachingClient when identifying the lowest TTL entry.

src/Ae.Dns.Client/DnsCachingClient.cs

@@ -21,7 +21,7 @@ private class DnsCacheEntry
         {
             public DnsCacheEntry(DnsMessage answer)
             {
-                var allRecords = new[] { answer.Answers, answer.Nameservers };
+                var allRecords = new[] { answer.Answers, answer.Nameservers, answer.Additional };
 
                 LowestRecordTimeToLive = TimeSpan.FromSeconds(allRecords.SelectMany(x => x).Min(x => x.TimeToLive));
                 Data = DnsByteExtensions.AllocateAndWrite(answer);

tests/Ae.Dns.Tests/Client/DnsCachingClientTests.cs

@@ -0,0 +1,66 @@
+using Ae.Dns.Client;
+using Ae.Dns.Protocol;
+using Ae.Dns.Protocol.Enums;
+using Ae.Dns.Protocol.Records;
+using Moq;
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Runtime.Caching;
+using System.Threading;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Ae.Dns.Tests.Client
+{
+    public sealed class DnsCachingClientTests : IDisposable
+    {
+        private readonly MockRepository _repository = new MockRepository(MockBehavior.Strict);
+
+        public void Dispose() => _repository.VerifyAll();
+
+        [Fact]
+        public async Task TestCacheEntryWithOnlyAdditionalRecords()
+        {
+            var mockClient = _repository.Create<IDnsClient>();
+
+            var query1 = DnsQueryFactory.CreateQuery("example.com", DnsQueryType.A);
+
+            // query1 will be passed through to the inner client
+            mockClient.Setup(x => x.Query(query1, CancellationToken.None))
+                .ReturnsAsync(new DnsMessage
+                {
+                    Additional = new List<DnsResourceRecord>
+                    {
+                        // This is an unrealistic example
+                        new DnsResourceRecord
+                        {
+                            Host = "example.com",
+                            Type = DnsQueryType.A,
+                            Resource = new DnsIpAddressResource{IPAddress = IPAddress.Loopback},
+                            TimeToLive = 5
+                        }
+                    },
+                    Header = new DnsHeader { AdditionalRecordCount = 1, Id = query1.Header.Id }
+                });
+
+            using var cache = new MemoryCache("wibble");
+
+            IDnsClient client = new DnsCachingClient(mockClient.Object, cache);
+
+            Assert.Empty(cache);
+
+            var answer1 = await client.Query(query1, CancellationToken.None);
+
+            Assert.Equal(query1.Header.Id, answer1.Header.Id);
+            Assert.Single(cache);
+
+            // Will be served from the cache
+            var query2 = DnsQueryFactory.CreateQuery("example.com", DnsQueryType.A);
+            var answer2 = await client.Query(query2, CancellationToken.None);
+
+            Assert.Equal(query2.Header.Id, answer2.Header.Id);
+            Assert.Single(cache);
+        }
+    }
+}